Piston accumulators are commercially available and are widely used in hydraulic systems in a variety of applications. For example, they are used for storing energy, emergency actuation, leaking oil compensation, volume compensation, shock absorption, pulsation damping, and the like.
Long-term behavior is of very great importance for economical and reliable use of these accumulators. To guarantee operating behavior which is satisfactory in this regard, it must be ensured that the oil overflow from the fluid side which normally contains hydraulic oil to the gas side is minimized over the entire service life. Current hydraulic accumulators do not meet this requirement to an adequate degree.
DE 14 50 347 A discloses a generic hydraulic accumulator with a piston which can be moved in the accumulator housing in its axial direction and which separates the gas side from the fluid side of the accumulator housing. The periphery of the piston has guide elements that interact with the wall of the accumulator housing, together with at least one sealing element offset in the axial direction to the guide elements. Between the guide element nearest the piston side bordering on the fluid side and the sealing element which is offset in the axial direction to the gas side and which is the next one following in the axial direction, a pressure equalization channel discharges on the periphery of the piston and forms in the piston a fluid path to the fluid side. The pressure equalization channel contains a device which reduces its passage cross-section. In the known solution, the piston is formed from two piston parts which are held at a distance to one another by an energy accumulator in the form of a compression spring and which are routed within the accumulator housing along a common guide rod forming a stop.
Due to the motion of the overall piston within the accumulator housing, there is a pressure difference between the fluid side and the intermediate space which is located on the periphery of the piston between the guide element on the fluid-side end of the piston and the sealing element which follows next in the axial direction. Due to this pressure difference, a volumetric flow into the intermediate space between the guide element and sealing element occurs over the guide element. Entrained dirt particles are deposited in this way between the guide element and the piston. Due to movement of the overall piston, these particles can lead to scratches which adversely affect the system. The described pressure equalization channel eliminates the problem in that when the piston moves, no pressure difference occurs on the guide element and thus a volumetric flow which may be loaded with dirt particles is not produced. In the known solution it is possible that when the piston moves, dirt particles which may have already collected on the inside wall of the accumulator housing are run over in piston movements to damage the piston.
To prevent this problem, the prior art (DE 36 19 457 A) suggested a cylindrical hydraulic accumulator for hydraulic systems, having an accumulator housing cylinder closed on its two faces. A floating piston in the housing cylinder divides the cylinder into two spaces. Towards its seal against the inside cylinder wall on the two ends of its outside wall, the piston has one recess each. In one recess, a respective groove-packing ring of elastomer is arranged, such that its annular groove is pointed toward the pertinent piston face. However, this measure is not sufficient for effectively deterring dirt particles. The known groove-packing rings each have in cross-section a tetragonal profile sectional area which undergoes transition toward the pertinent face of the piston into a U-shaped profile cross-sectional area. The U-shaped profile cross-sectional area projects radially over the tetragonal profile cross-sectional area as a plain compression ring. The tetragonal profile cross-sectional area in its entire width is enclosed by a support ring of a high-strength material, preferably of a carbon fiber winding bonded in resin, with an outer surface which adjoins the inside cylinder wall, sliding almost without play. In the U-profile area which is left clear, dirt can collect which can adversely affect the sealing function. The projecting angular stripper edge of the seal, which edge is configured to be solid, is designed too stiffly for an effective sealing and stripping function.